The present invention relates to a serial printer of the type with a carriage which can move along a print line and with a character carrying element which can rotate on the carriage and remain stationary during printing.
Serial printers of this type are known wherein, in order to raise the printing speed the carriage is not braked when it comes level with the printing position: what is known as "on-the-fly printing" is performed. So that the selected character can be printed exactly on the predetermined printing point, the carriage is moved at a speed such that the selection can be completed. Selection times being equal the maximum printing speed will therefore be reached if the time taken by the character carrying element to select the character to be typed is equal to the time taken by the carriage to arrive at the intended printing position. This is achieved by various ways of timing the movement of the carriage and that of the character carrying element. In particular the carriage can move, between one printing position and the next, according to speed profiles which are predetermined and chosen as a function of the angle of rotation of the character carrying element.
This solution comprises a very complex unit for the control of the movements of the carriage or of the character carrying element. Moreover, since the real behaviour, electrical or physical, of the devices which make up the printer differs from that which could be provided theoretically, the speed of the carriage has to be controlled with a certain safety margin. This margin becomes manifested in a reduction in printing speed; this is because the carriage must not overrun the printing point before completion of the selection of the character which is to be printed. This is of particular importance when long shifts are involved (also fast shifts) for the carriage, as for example during tabulating or carriage return.
The technical problem of the present invention is to provide a control unit to synchronize the movements of the carriage and of the character carrying element in cases of normal writing and/or in cases of tabulating or carriage return. Said control unit is simple, cheap, and capable of controlling continuously, precisely and optimally the speed of the carriage as a function of the real kinetic behavior of the character carrying element with the object of obtaining optimal printing speed.